The present invention relates to a pressure reduction valve for a compressible fluid.
Pressure reduction valves for reducing the pressure of a fluid i.e. a gas, liquid or vapour are well known. One such example, described in our UK Patent No. 1405850, has a pressure reduction member disposed between the inlet and outlet chambers of a valve. The pressure reduction member comprises a plurality of concentric spaced sleeves each being penetrated by radial passages. High pressure fluid enters the inlet, passes through radial passages in a first sleeve and then expands into an annular clearance between sleeves to result in a reduction of fluid pressure. This process is repeated several times through successive sleeves until the fluid reaches the outlet at low pressure.
Existing pressure reduction valves have the disadvantage of requiring a number of expensive control elements. Each element, does of itself generate some noise, but the overall effect is a reduction in noise level due to the reduction in fluid velocity which reduces or eliminates shock waves.
In view of increasing concern for the environment reflected in pending legislation, it is desirable to reduce objectionable noise and to be able to achieve this in the most economical manner.
U.S. Pat. No. 4,041,982 describes a control valve with a double-walled pressure reduction cage. The cage has a pair of perforated cylindrical walls spaced apart in a concentric relationship. A reciprocal valve plug is disposed between the walls to control the fluid flow though the valve. The perforations in the cylinders are of constant diameter and provide a two-stage reduction. Further reduction in pressure occurs during free expansion of the fluid outside of the cage, such expansion will include shock waves.
It is an object of the present invention to provide for a pressure reduction valve that brings about a reduction in noise normally generated by a fluid when undergoing pressure reduction and to achieve this without resorting to numerous sleeves or large diameter discs forming tortuous paths.
According to the present invention there is provided a pressure reduction valve for a compressible fluid, the valve comprising an inlet and outlet separated by a pressure reduction member having a plurality of nozzles, a diffuser, an attenuation chamber intermediate the pressure reduction member and the diffuser, and a plug that is movable to close one or more nozzles so as to control the amount of flow of the compressible fluid from the inlet to the outlet characterised in that the nozzles are convergent-divergent nozzles in the direction of flow of the compressible fluid, and that the attenuation chamber is disposed downstream of the plug, so that its volume is sufficient for attenuating the noise from the turbulence of jets of compressible fluid emergent from the nozzles independently of the position of the plug.
High pressure gas or vapour passes from the valve inlet through the nozzles which control the expansion of the gas/vapour to a reduced pressure and eliminate shock waves. The gas/vapour expands into the intermediate attenuation chamber in which the resulting turbulence is confined before the gas/vapour passes through the diffuser into the outlet such that the diffused streams do not interact.
Preferably the pressure reduction member and the diffuser are concentric cylinders spaced apart to define the intermediate attenuation chamber.
The nozzles may be arranged in axially spaced circumferential rows.
The plug may be axially slidable along an inner surface of the pressure reduction member.